1. Field of the Invention
The present invention is related to passenger detection systems, and in particular to passenger detection systems that can readily detect the presence of a passenger in the front passenger seat of an automobile in which a passenger-side air bag device is installed.
2. Description of the Prior Art
In general, air bag devices are used to ease the shock that a passenger experiences during an automobile collision, and as such must be stored in a stable condition in the automobile. Air bags are typically installed in front of the driver's seat, but there has been a recent trend toward installing a second air bag device in front of the front passenger seat.
FIG. 14 shows a prior art air bag control system for controlling the deployment of driver-side and passenger-side air bag devices. The control system includes a control circuit CC that receives a signal from an electrical acceleration sensor (shock detection sensor) GS, and transmits control signals to the gates of normally-open semiconductor switching elements SW1 and SW2. Switching elements SW1 and SW2 are respectively connected in parallel paths between a system operating voltage and ground. The first path includes a safing sensor SS1, a squib circuit SQ1 and the switching element SW1. The second path includes a safing sensor SS2, a squib circuit SQ2 and the switching element SW2. The safing sensors SS1 and SS2 are respectively mounted on the driver's seat and the front passenger seat, and each includes an acceleration detection mechanism that closes a normally-open switch in response to sudden acceleration (deceleration) of the respective seat. Squib circuits SQ1 and SQ2 are connected to the gas sources of the air bag devices respectively mounted on the automobile in front of the driver's seat and the front passenger seat.
In operation, the prior art air bag control system only deploys the driver-side and passenger side air bags when both of the safing sensors SS1 and SS2 close, and when the electrical acceleration sensor GS closes. In particular, the acceleration detection mechanisms of the safing sensors SS1 and SS2 close their respective normally-open switches in response to an acceleration that is relatively small in comparison to the acceleration necessary to close the electrical acceleration sensor GS. When closed, the safing sensors SS1 and SS2 apply a high voltage signal to the control circuit CC and to first terminals of the squib circuits SQ1 and SQ2. The high voltage signals from the safing sensors SS1 and SS2 cause the control circuit CC to enter into an operational mode. Next, the control circuit CC confirms that the automobile is in an accident based on the signal from the electrical acceleration sensor GS. If the electrical acceleration sensor GS also detects the acceleration, thereby confirming that the automobile is actually in a collision, then the control circuit CC transmits control signals that close the switching elements SW1 and SW2. As a result, current flows from the system operating voltage to ground through each of the squib circuits SQ1 and SQ2, thereby causing respective gas sources to deploy (inflate) the driver-side air bag and the passenger-side air bag. Once deployed, the air bags protect the driver and passenger from the shock of the collision.
The air bag control system is designed to protect an adult passenger during a collision, but can cause serious injury when deployed while a child or infant is in the front passenger seat. Referring to FIG. 15(a), a passenger-side air bag is typically designed to deploy in front of the torso of an adult passenger P seated in the front passenger seat 1, thereby cushioning the forward acceleration of the adult passenger P during a collision. However, as shown in FIG. 15(b), if an infant (small passenger) SP is in a rear facing infant seat (hereafter abbreviated RFIS) 1A that is located on the front passenger seat 1, deployment of the passenger-side air bag can force the RFIS 1A toward the seat back, which can injure the infant. Consequently, when an RFIS is located on the front passenger seat, it is desirable for the passenger-side air bag not to deploy even if the automobile is in a collision. In addition, as shown in FIG. 15(c), the head of a child SP seated in a forward facing child seat (hereafter abbreviated FFCS) 1A is typically lower and further forward than that of an adult passenger P, so that the deploying air bag can injure the child SP. Consequently, it is also desirable for the passenger-side air bag not to deploy when a FFCS is used, even in the event of a collision.
FIG. 16 shows a prior art air bag control system that prevents deployment of the passenger-side air bag when an RFIS or FFCS is used. This air bag control system includes a passenger detection sensor SD for detecting whether or not a passenger is seated in the front passenger seat. Further, based on the detection signal from sensor SD, the control circuit CC determines whether the passenger seated in the front passenger seat is an adult or a child. The air bag control system deploys the air bag during a collision only if sensor SD generates a detection signal that indicates an adult passenger is seated in the front passenger seat.
Several passenger detection sensor types have been proposed for implementing sensor SD in the air bag control system of FIG. 16. Such proposed sensors include a weight-based unit that measures the weight applied to the front passenger seat, and an optics-based unit that determines whether the passenger is an adult P or a child SP by generating an image of the passenger seated in the seat, and then processing the image.
The weight-based sensor unit provides a broad determination about whether the passenger in a front passenger seat is an adult or a child based on the weight applied to the seat, but cannot distinguish between an adult/child and an inanimate object. In particular, the air bag control system prevents deployment of the air bag when the detected weight is less than that associated with an adult. However, although this can avoid undesirable circumstances during an automobile collision when a small child is seated in the front passenger seat, the weight-based unit may incorrectly deploy for a heavy child, or fail to deploy for a light-weight adult. Further, if a heavy object (such as a bag of groceries) is placed on the seat, the air bag device may be needlessly deployed in an accident.
The optical-based sensor unit can provide very accurate determinations about the passenger seated in the front passenger seat by processing the image data taken by the camera and then comparing the processed data with various patterns. For example, the image data may be compared with data consistent with an adult passenger, a child in a RFIS, or a child in a FFCS. However, this unit has a problem in that it is very expensive and the processing equipment is very complex.